To follow the example set by Jesus.
At that time Jesus came from Nazareth in Galilee and was baptized by John in the Jordan.
— Mark 1:9
Because Jesus commanded it.
Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, and teaching them to obey everything I have commanded you. And surely I am with you always, to the very end of the age.
— Matthew 28:19–20
It shows I really do believe in Jesus.
We know that we have come to know him if we keep his commands.
— 1 John 2:3